1 /* 2 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. Oracle designates this 8 * particular file as subject to the "Classpath" exception as provided 9 * by Oracle in the LICENSE file that accompanied this code. 10 * 11 * This code is distributed in the hope that it will be useful, but WITHOUT 12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 14 * version 2 for more details (a copy is included in the LICENSE file that 15 * accompanied this code). 16 * 17 * You should have received a copy of the GNU General Public License version 18 * 2 along with this work; if not, write to the Free Software Foundation, 19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 20 * 21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 22 * or visit www.oracle.com if you need additional information or have any 23 * questions. 24 */ 25 26 package java.lang; 27 import java.io.*; 28 import java.util.*; 29 30 /** 31 * The {@code Throwable} class is the superclass of all errors and 32 * exceptions in the Java language. Only objects that are instances of this 33 * class (or one of its subclasses) are thrown by the Java Virtual Machine or 34 * can be thrown by the Java {@code throw} statement. Similarly, only 35 * this class or one of its subclasses can be the argument type in a 36 * {@code catch} clause. 37 * 38 * For the purposes of compile-time checking of exceptions, {@code 39 * Throwable} and any subclass of {@code Throwable} that is not also a 40 * subclass of either {@link RuntimeException} or {@link Error} are 41 * regarded as checked exceptions. 42 * 43 * <p>Instances of two subclasses, {@link java.lang.Error} and 44 * {@link java.lang.Exception}, are conventionally used to indicate 45 * that exceptional situations have occurred. Typically, these instances 46 * are freshly created in the context of the exceptional situation so 47 * as to include relevant information (such as stack trace data). 48 * 49 * <p>A throwable contains a snapshot of the execution stack of its 50 * thread at the time it was created. It can also contain a message 51 * string that gives more information about the error. Over time, a 52 * throwable can {@linkplain Throwable#addSuppressed suppress} other 53 * throwables from being propagated. Finally, the throwable can also 54 * contain a <i>cause</i>: another throwable that caused this 55 * throwable to be constructed. The recording of this causal information 56 * is referred to as the <i>chained exception</i> facility, as the 57 * cause can, itself, have a cause, and so on, leading to a "chain" of 58 * exceptions, each caused by another. 59 * 60 * <p>One reason that a throwable may have a cause is that the class that 61 * throws it is built atop a lower layered abstraction, and an operation on 62 * the upper layer fails due to a failure in the lower layer. It would be bad 63 * design to let the throwable thrown by the lower layer propagate outward, as 64 * it is generally unrelated to the abstraction provided by the upper layer. 65 * Further, doing so would tie the API of the upper layer to the details of 66 * its implementation, assuming the lower layer's exception was a checked 67 * exception. Throwing a "wrapped exception" (i.e., an exception containing a 68 * cause) allows the upper layer to communicate the details of the failure to 69 * its caller without incurring either of these shortcomings. It preserves 70 * the flexibility to change the implementation of the upper layer without 71 * changing its API (in particular, the set of exceptions thrown by its 72 * methods). 73 * 74 * <p>A second reason that a throwable may have a cause is that the method 75 * that throws it must conform to a general-purpose interface that does not 76 * permit the method to throw the cause directly. For example, suppose 77 * a persistent collection conforms to the {@link java.util.Collection 78 * Collection} interface, and that its persistence is implemented atop 79 * {@code java.io}. Suppose the internals of the {@code add} method 80 * can throw an {@link java.io.IOException IOException}. The implementation 81 * can communicate the details of the {@code IOException} to its caller 82 * while conforming to the {@code Collection} interface by wrapping the 83 * {@code IOException} in an appropriate unchecked exception. (The 84 * specification for the persistent collection should indicate that it is 85 * capable of throwing such exceptions.) 86 * 87 * <p>A cause can be associated with a throwable in two ways: via a 88 * constructor that takes the cause as an argument, or via the 89 * {@link #initCause(Throwable)} method. New throwable classes that 90 * wish to allow causes to be associated with them should provide constructors 91 * that take a cause and delegate (perhaps indirectly) to one of the 92 * {@code Throwable} constructors that takes a cause. 93 * 94 * Because the {@code initCause} method is public, it allows a cause to be 95 * associated with any throwable, even a "legacy throwable" whose 96 * implementation predates the addition of the exception chaining mechanism to 97 * {@code Throwable}. 98 * 99 * <p>By convention, class {@code Throwable} and its subclasses have two 100 * constructors, one that takes no arguments and one that takes a 101 * {@code String} argument that can be used to produce a detail message. 102 * Further, those subclasses that might likely have a cause associated with 103 * them should have two more constructors, one that takes a 104 * {@code Throwable} (the cause), and one that takes a 105 * {@code String} (the detail message) and a {@code Throwable} (the 106 * cause). 107 * 108 * @author unascribed 109 * @author Josh Bloch (Added exception chaining and programmatic access to 110 * stack trace in 1.4.) 111 * @jls 11.2 Compile-Time Checking of Exceptions 112 * @since JDK1.0 113 */ 114 public class Throwable implements Serializable { 115 /** use serialVersionUID from JDK 1.0.2 for interoperability */ 116 private static final long serialVersionUID = -3042686055658047285L; 117 118 /** 119 * Native code saves some indication of the stack backtrace in this slot. 120 */ 121 private transient Object backtrace; 122 123 /** 124 * Specific details about the Throwable. For example, for 125 * {@code FileNotFoundException}, this contains the name of 126 * the file that could not be found. 127 * 128 * @serial 129 */ 130 private String detailMessage; 131 132 133 /** 134 * Holder class to defer initializing sentinel objects only used 135 * for serialization. 136 */ 137 private static class SentinelHolder { 138 /** 139 * {@linkplain #setStackTrace(StackTraceElement[]) Setting the 140 * stack trace} to a one-element array containing this sentinel 141 * value indicates future attempts to set the stack trace will be 142 * ignored. The sentinal is equal to the result of calling:<br> 143 * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)} 144 */ 145 public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL = 146 new StackTraceElement("", "", null, Integer.MIN_VALUE); 147 148 /** 149 * Sentinel value used in the serial form to indicate an immutable 150 * stack trace. 151 */ 152 public static final StackTraceElement[] STACK_TRACE_SENTINEL = 153 new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL}; 154 } 155 156 /** 157 * A shared value for an empty stack. 158 */ 159 private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0]; 160 161 /* 162 * To allow Throwable objects to be made immutable and safely 163 * reused by the JVM, such as OutOfMemoryErrors, fields of 164 * Throwable that are writable in response to user actions, cause, 165 * stackTrace, and suppressedExceptions obey the following 166 * protocol: 167 * 168 * 1) The fields are initialized to a non-null sentinel value 169 * which indicates the value has logically not been set. 170 * 171 * 2) Writing a null to the field indicates further writes 172 * are forbidden 173 * 174 * 3) The sentinel value may be replaced with another non-null 175 * value. 176 * 177 * For example, implementations of the HotSpot JVM have 178 * preallocated OutOfMemoryError objects to provide for better 179 * diagnosability of that situation. These objects are created 180 * without calling the constructor for that class and the fields 181 * in question are initialized to null. To support this 182 * capability, any new fields added to Throwable that require 183 * being initialized to a non-null value require a coordinated JVM 184 * change. 185 */ 186 187 /** 188 * The throwable that caused this throwable to get thrown, or null if this 189 * throwable was not caused by another throwable, or if the causative 190 * throwable is unknown. If this field is equal to this throwable itself, 191 * it indicates that the cause of this throwable has not yet been 192 * initialized. 193 * 194 * @serial 195 * @since 1.4 196 */ 197 private Throwable cause = this; 198 199 /** 200 * The stack trace, as returned by {@link #getStackTrace()}. 201 * 202 * The field is initialized to a zero-length array. A {@code 203 * null} value of this field indicates subsequent calls to {@link 204 * #setStackTrace(StackTraceElement[])} and {@link 205 * #fillInStackTrace()} will be be no-ops. 206 * 207 * @serial 208 * @since 1.4 209 */ 210 private StackTraceElement[] stackTrace = UNASSIGNED_STACK; 211 212 // Setting this static field introduces an acceptable 213 // initialization dependency on a few java.util classes. 214 private static final List<Throwable> SUPPRESSED_SENTINEL = 215 Collections.unmodifiableList(new ArrayList<Throwable>(0)); 216 217 /** 218 * The list of suppressed exceptions, as returned by {@link 219 * #getSuppressed()}. The list is initialized to a zero-element 220 * unmodifiable sentinel list. When a serialized Throwable is 221 * read in, if the {@code suppressedExceptions} field points to a 222 * zero-element list, the field is reset to the sentinel value. 223 * 224 * @serial 225 * @since 1.7 226 */ 227 private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL; 228 229 /** Message for trying to suppress a null exception. */ 230 private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception."; 231 232 /** Message for trying to suppress oneself. */ 233 private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted"; 234 235 /** Caption for labeling causative exception stack traces */ 236 private static final String CAUSE_CAPTION = "Caused by: "; 237 238 /** Caption for labeling suppressed exception stack traces */ 239 private static final String SUPPRESSED_CAPTION = "Suppressed: "; 240 241 /** 242 * Constructs a new throwable with {@code null} as its detail message. 243 * The cause is not initialized, and may subsequently be initialized by a 244 * call to {@link #initCause}. 245 * 246 * <p>The {@link #fillInStackTrace()} method is called to initialize 247 * the stack trace data in the newly created throwable. 248 */ 249 public Throwable() { 250 fillInStackTrace(); 251 } 252 253 /** 254 * Constructs a new throwable with the specified detail message. The 255 * cause is not initialized, and may subsequently be initialized by 256 * a call to {@link #initCause}. 257 * 258 * <p>The {@link #fillInStackTrace()} method is called to initialize 259 * the stack trace data in the newly created throwable. 260 * 261 * @param message the detail message. The detail message is saved for 262 * later retrieval by the {@link #getMessage()} method. 263 */ 264 public Throwable(String message) { 265 fillInStackTrace(); 266 detailMessage = message; 267 } 268 269 /** 270 * Constructs a new throwable with the specified detail message and 271 * cause. <p>Note that the detail message associated with 272 * {@code cause} is <i>not</i> automatically incorporated in 273 * this throwable's detail message. 274 * 275 * <p>The {@link #fillInStackTrace()} method is called to initialize 276 * the stack trace data in the newly created throwable. 277 * 278 * @param message the detail message (which is saved for later retrieval 279 * by the {@link #getMessage()} method). 280 * @param cause the cause (which is saved for later retrieval by the 281 * {@link #getCause()} method). (A {@code null} value is 282 * permitted, and indicates that the cause is nonexistent or 283 * unknown.) 284 * @since 1.4 285 */ 286 public Throwable(String message, Throwable cause) { 287 fillInStackTrace(); 288 detailMessage = message; 289 this.cause = cause; 290 } 291 292 /** 293 * Constructs a new throwable with the specified cause and a detail 294 * message of {@code (cause==null ? null : cause.toString())} (which 295 * typically contains the class and detail message of {@code cause}). 296 * This constructor is useful for throwables that are little more than 297 * wrappers for other throwables (for example, {@link 298 * java.security.PrivilegedActionException}). 299 * 300 * <p>The {@link #fillInStackTrace()} method is called to initialize 301 * the stack trace data in the newly created throwable. 302 * 303 * @param cause the cause (which is saved for later retrieval by the 304 * {@link #getCause()} method). (A {@code null} value is 305 * permitted, and indicates that the cause is nonexistent or 306 * unknown.) 307 * @since 1.4 308 */ 309 public Throwable(Throwable cause) { 310 fillInStackTrace(); 311 detailMessage = (cause==null ? null : cause.toString()); 312 this.cause = cause; 313 } 314 315 /** 316 * Constructs a new throwable with the specified detail message, 317 * cause, {@linkplain #addSuppressed suppression} enabled or 318 * disabled, and writable stack trace enabled or disabled. If 319 * suppression is disabled, {@link #getSuppressed} for this object 320 * will return a zero-length array and calls to {@link 321 * #addSuppressed} that would otherwise append an exception to the 322 * suppressed list will have no effect. If the writable stack 323 * trace is false, this constructor will not call {@link 324 * #fillInStackTrace()}, a {@code null} will be written to the 325 * {@code stackTrace} field, and subsequent calls to {@code 326 * fillInStackTrace} and {@link 327 * #setStackTrace(StackTraceElement[])} will not set the stack 328 * trace. If the writable stack trace is false, {@link 329 * #getStackTrace} will return a zero length array. 330 * 331 * <p>Note that the other constructors of {@code Throwable} treat 332 * suppression as being enabled and the stack trace as being 333 * writable. Subclasses of {@code Throwable} should document any 334 * conditions under which suppression is disabled and document 335 * conditions under which the stack trace is not writable. 336 * Disabling of suppression should only occur in exceptional 337 * circumstances where special requirements exist, such as a 338 * virtual machine reusing exception objects under low-memory 339 * situations. Circumstances where a given exception object is 340 * repeatedly caught and rethrown, such as to implement control 341 * flow between two sub-systems, is another situation where 342 * immutable throwable objects would be appropriate. 343 * 344 * @param message the detail message. 345 * @param cause the cause. (A {@code null} value is permitted, 346 * and indicates that the cause is nonexistent or unknown.) 347 * @param enableSuppression whether or not suppression is enabled or disabled 348 * @param writableStackTrace whether or not the stack trace should be 349 * writable 350 * 351 * @see OutOfMemoryError 352 * @see NullPointerException 353 * @see ArithmeticException 354 * @since 1.7 355 */ 356 protected Throwable(String message, Throwable cause, 357 boolean enableSuppression, 358 boolean writableStackTrace) { 359 if (writableStackTrace) { 360 fillInStackTrace(); 361 } else { 362 stackTrace = null; 363 } 364 detailMessage = message; 365 this.cause = cause; 366 if (!enableSuppression) 367 suppressedExceptions = null; 368 } 369 370 /** 371 * Returns the detail message string of this throwable. 372 * 373 * @return the detail message string of this {@code Throwable} instance 374 * (which may be {@code null}). 375 */ 376 public String getMessage() { 377 return detailMessage; 378 } 379 380 /** 381 * Creates a localized description of this throwable. 382 * Subclasses may override this method in order to produce a 383 * locale-specific message. For subclasses that do not override this 384 * method, the default implementation returns the same result as 385 * {@code getMessage()}. 386 * 387 * @return The localized description of this throwable. 388 * @since JDK1.1 389 */ 390 public String getLocalizedMessage() { 391 return getMessage(); 392 } 393 394 /** 395 * Returns the cause of this throwable or {@code null} if the 396 * cause is nonexistent or unknown. (The cause is the throwable that 397 * caused this throwable to get thrown.) 398 * 399 * <p>This implementation returns the cause that was supplied via one of 400 * the constructors requiring a {@code Throwable}, or that was set after 401 * creation with the {@link #initCause(Throwable)} method. While it is 402 * typically unnecessary to override this method, a subclass can override 403 * it to return a cause set by some other means. This is appropriate for 404 * a "legacy chained throwable" that predates the addition of chained 405 * exceptions to {@code Throwable}. Note that it is <i>not</i> 406 * necessary to override any of the {@code PrintStackTrace} methods, 407 * all of which invoke the {@code getCause} method to determine the 408 * cause of a throwable. 409 * 410 * @return the cause of this throwable or {@code null} if the 411 * cause is nonexistent or unknown. 412 * @since 1.4 413 */ 414 public synchronized Throwable getCause() { 415 return (cause==this ? null : cause); 416 } 417 418 /** 419 * Initializes the <i>cause</i> of this throwable to the specified value. 420 * (The cause is the throwable that caused this throwable to get thrown.) 421 * 422 * <p>This method can be called at most once. It is generally called from 423 * within the constructor, or immediately after creating the 424 * throwable. If this throwable was created 425 * with {@link #Throwable(Throwable)} or 426 * {@link #Throwable(String,Throwable)}, this method cannot be called 427 * even once. 428 * 429 * <p>An example of using this method on a legacy throwable type 430 * without other support for setting the cause is: 431 * 432 * <pre> 433 * try { 434 * lowLevelOp(); 435 * } catch (LowLevelException le) { 436 * throw (HighLevelException) 437 * new HighLevelException().initCause(le); // Legacy constructor 438 * } 439 * </pre> 440 * 441 * @param cause the cause (which is saved for later retrieval by the 442 * {@link #getCause()} method). (A {@code null} value is 443 * permitted, and indicates that the cause is nonexistent or 444 * unknown.) 445 * @return a reference to this {@code Throwable} instance. 446 * @throws IllegalArgumentException if {@code cause} is this 447 * throwable. (A throwable cannot be its own cause.) 448 * @throws IllegalStateException if this throwable was 449 * created with {@link #Throwable(Throwable)} or 450 * {@link #Throwable(String,Throwable)}, or this method has already 451 * been called on this throwable. 452 * @since 1.4 453 */ 454 public synchronized Throwable initCause(Throwable cause) { 455 if (this.cause != this) 456 throw new IllegalStateException("Can't overwrite cause with " + 457 Objects.toString(cause, "a null"), this); 458 if (cause == this) 459 throw new IllegalArgumentException("Self-causation not permitted", this); 460 this.cause = cause; 461 return this; 462 } 463 464 /** 465 * Returns a short description of this throwable. 466 * The result is the concatenation of: 467 * <ul> 468 * <li> the {@linkplain Class#getName() name} of the class of this object 469 * <li> ": " (a colon and a space) 470 * <li> the result of invoking this object's {@link #getLocalizedMessage} 471 * method 472 * </ul> 473 * If {@code getLocalizedMessage} returns {@code null}, then just 474 * the class name is returned. 475 * 476 * @return a string representation of this throwable. 477 */ 478 public String toString() { 479 String s = getClass().getName(); 480 String message = getLocalizedMessage(); 481 return (message != null) ? (s + ": " + message) : s; 482 } 483 484 /** 485 * Prints this throwable and its backtrace to the 486 * standard error stream. This method prints a stack trace for this 487 * {@code Throwable} object on the error output stream that is 488 * the value of the field {@code System.err}. The first line of 489 * output contains the result of the {@link #toString()} method for 490 * this object. Remaining lines represent data previously recorded by 491 * the method {@link #fillInStackTrace()}. The format of this 492 * information depends on the implementation, but the following 493 * example may be regarded as typical: 494 * <blockquote><pre> 495 * java.lang.NullPointerException 496 * at MyClass.mash(MyClass.java:9) 497 * at MyClass.crunch(MyClass.java:6) 498 * at MyClass.main(MyClass.java:3) 499 * </pre></blockquote> 500 * This example was produced by running the program: 501 * <pre> 502 * class MyClass { 503 * public static void main(String[] args) { 504 * crunch(null); 505 * } 506 * static void crunch(int[] a) { 507 * mash(a); 508 * } 509 * static void mash(int[] b) { 510 * System.out.println(b[0]); 511 * } 512 * } 513 * </pre> 514 * The backtrace for a throwable with an initialized, non-null cause 515 * should generally include the backtrace for the cause. The format 516 * of this information depends on the implementation, but the following 517 * example may be regarded as typical: 518 * <pre> 519 * HighLevelException: MidLevelException: LowLevelException 520 * at Junk.a(Junk.java:13) 521 * at Junk.main(Junk.java:4) 522 * Caused by: MidLevelException: LowLevelException 523 * at Junk.c(Junk.java:23) 524 * at Junk.b(Junk.java:17) 525 * at Junk.a(Junk.java:11) 526 * ... 1 more 527 * Caused by: LowLevelException 528 * at Junk.e(Junk.java:30) 529 * at Junk.d(Junk.java:27) 530 * at Junk.c(Junk.java:21) 531 * ... 3 more 532 * </pre> 533 * Note the presence of lines containing the characters {@code "..."}. 534 * These lines indicate that the remainder of the stack trace for this 535 * exception matches the indicated number of frames from the bottom of the 536 * stack trace of the exception that was caused by this exception (the 537 * "enclosing" exception). This shorthand can greatly reduce the length 538 * of the output in the common case where a wrapped exception is thrown 539 * from same method as the "causative exception" is caught. The above 540 * example was produced by running the program: 541 * <pre> 542 * public class Junk { 543 * public static void main(String args[]) { 544 * try { 545 * a(); 546 * } catch(HighLevelException e) { 547 * e.printStackTrace(); 548 * } 549 * } 550 * static void a() throws HighLevelException { 551 * try { 552 * b(); 553 * } catch(MidLevelException e) { 554 * throw new HighLevelException(e); 555 * } 556 * } 557 * static void b() throws MidLevelException { 558 * c(); 559 * } 560 * static void c() throws MidLevelException { 561 * try { 562 * d(); 563 * } catch(LowLevelException e) { 564 * throw new MidLevelException(e); 565 * } 566 * } 567 * static void d() throws LowLevelException { 568 * e(); 569 * } 570 * static void e() throws LowLevelException { 571 * throw new LowLevelException(); 572 * } 573 * } 574 * 575 * class HighLevelException extends Exception { 576 * HighLevelException(Throwable cause) { super(cause); } 577 * } 578 * 579 * class MidLevelException extends Exception { 580 * MidLevelException(Throwable cause) { super(cause); } 581 * } 582 * 583 * class LowLevelException extends Exception { 584 * } 585 * </pre> 586 * As of release 7, the platform supports the notion of 587 * <i>suppressed exceptions</i> (in conjunction with the {@code 588 * try}-with-resources statement). Any exceptions that were 589 * suppressed in order to deliver an exception are printed out 590 * beneath the stack trace. The format of this information 591 * depends on the implementation, but the following example may be 592 * regarded as typical: 593 * 594 * <pre> 595 * Exception in thread "main" java.lang.Exception: Something happened 596 * at Foo.bar(Foo.java:10) 597 * at Foo.main(Foo.java:5) 598 * Suppressed: Resource$CloseFailException: Resource ID = 0 599 * at Resource.close(Resource.java:26) 600 * at Foo.bar(Foo.java:9) 601 * ... 1 more 602 * </pre> 603 * Note that the "... n more" notation is used on suppressed exceptions 604 * just at it is used on causes. Unlike causes, suppressed exceptions are 605 * indented beyond their "containing exceptions." 606 * 607 * <p>An exception can have both a cause and one or more suppressed 608 * exceptions: 609 * <pre> 610 * Exception in thread "main" java.lang.Exception: Main block 611 * at Foo3.main(Foo3.java:7) 612 * Suppressed: Resource$CloseFailException: Resource ID = 2 613 * at Resource.close(Resource.java:26) 614 * at Foo3.main(Foo3.java:5) 615 * Suppressed: Resource$CloseFailException: Resource ID = 1 616 * at Resource.close(Resource.java:26) 617 * at Foo3.main(Foo3.java:5) 618 * Caused by: java.lang.Exception: I did it 619 * at Foo3.main(Foo3.java:8) 620 * </pre> 621 * Likewise, a suppressed exception can have a cause: 622 * <pre> 623 * Exception in thread "main" java.lang.Exception: Main block 624 * at Foo4.main(Foo4.java:6) 625 * Suppressed: Resource2$CloseFailException: Resource ID = 1 626 * at Resource2.close(Resource2.java:20) 627 * at Foo4.main(Foo4.java:5) 628 * Caused by: java.lang.Exception: Rats, you caught me 629 * at Resource2$CloseFailException.<init>(Resource2.java:45) 630 * ... 2 more 631 * </pre> 632 */ 633 public void printStackTrace() { 634 printStackTrace(System.err); 635 } 636 637 /** 638 * Prints this throwable and its backtrace to the specified print stream. 639 * 640 * @param s {@code PrintStream} to use for output 641 */ 642 public void printStackTrace(PrintStream s) { 643 printStackTrace(new WrappedPrintStream(s)); 644 } 645 646 private void printStackTrace(PrintStreamOrWriter s) { 647 // Guard against malicious overrides of Throwable.equals by 648 // using a Set with identity equality semantics. 649 Set<Throwable> dejaVu = Collections.newSetFromMap(new IdentityHashMap<>()); 650 dejaVu.add(this); 651 652 synchronized (s.lock()) { 653 // Print our stack trace 654 s.println(this); 655 StackTraceElement[] trace = getOurStackTrace(); 656 for (StackTraceElement traceElement : trace) 657 s.println("\tat " + traceElement); 658 659 // Print suppressed exceptions, if any 660 for (Throwable se : getSuppressed()) 661 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); 662 663 // Print cause, if any 664 Throwable ourCause = getCause(); 665 if (ourCause != null) 666 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu); 667 } 668 } 669 670 /** 671 * Print our stack trace as an enclosed exception for the specified 672 * stack trace. 673 */ 674 private void printEnclosedStackTrace(PrintStreamOrWriter s, 675 StackTraceElement[] enclosingTrace, 676 String caption, 677 String prefix, 678 Set<Throwable> dejaVu) { 679 assert Thread.holdsLock(s.lock()); 680 if (dejaVu.contains(this)) { 681 s.println("\t[CIRCULAR REFERENCE:" + this + "]"); 682 } else { 683 dejaVu.add(this); 684 // Compute number of frames in common between this and enclosing trace 685 StackTraceElement[] trace = getOurStackTrace(); 686 int m = trace.length - 1; 687 int n = enclosingTrace.length - 1; 688 while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { 689 m--; n--; 690 } 691 int framesInCommon = trace.length - 1 - m; 692 693 // Print our stack trace 694 s.println(prefix + caption + this); 695 for (int i = 0; i <= m; i++) 696 s.println(prefix + "\tat " + trace[i]); 697 if (framesInCommon != 0) 698 s.println(prefix + "\t... " + framesInCommon + " more"); 699 700 // Print suppressed exceptions, if any 701 for (Throwable se : getSuppressed()) 702 se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, 703 prefix +"\t", dejaVu); 704 705 // Print cause, if any 706 Throwable ourCause = getCause(); 707 if (ourCause != null) 708 ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu); 709 } 710 } 711 712 /** 713 * Prints this throwable and its backtrace to the specified 714 * print writer. 715 * 716 * @param s {@code PrintWriter} to use for output 717 * @since JDK1.1 718 */ 719 public void printStackTrace(PrintWriter s) { 720 printStackTrace(new WrappedPrintWriter(s)); 721 } 722 723 /** 724 * Wrapper class for PrintStream and PrintWriter to enable a single 725 * implementation of printStackTrace. 726 */ 727 private abstract static class PrintStreamOrWriter { 728 /** Returns the object to be locked when using this StreamOrWriter */ 729 abstract Object lock(); 730 731 /** Prints the specified string as a line on this StreamOrWriter */ 732 abstract void println(Object o); 733 } 734 735 private static class WrappedPrintStream extends PrintStreamOrWriter { 736 private final PrintStream printStream; 737 738 WrappedPrintStream(PrintStream printStream) { 739 this.printStream = printStream; 740 } 741 742 Object lock() { 743 return printStream; 744 } 745 746 void println(Object o) { 747 printStream.println(o); 748 } 749 } 750 751 private static class WrappedPrintWriter extends PrintStreamOrWriter { 752 private final PrintWriter printWriter; 753 754 WrappedPrintWriter(PrintWriter printWriter) { 755 this.printWriter = printWriter; 756 } 757 758 Object lock() { 759 return printWriter; 760 } 761 762 void println(Object o) { 763 printWriter.println(o); 764 } 765 } 766 767 /** 768 * Fills in the execution stack trace. This method records within this 769 * {@code Throwable} object information about the current state of 770 * the stack frames for the current thread. 771 * 772 * <p>If the stack trace of this {@code Throwable} {@linkplain 773 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 774 * writable}, calling this method has no effect. 775 * 776 * @return a reference to this {@code Throwable} instance. 777 * @see java.lang.Throwable#printStackTrace() 778 */ 779 public synchronized Throwable fillInStackTrace() { 780 if (stackTrace != null || 781 backtrace != null /* Out of protocol state */ ) { 782 fillInStackTrace(0); 783 stackTrace = UNASSIGNED_STACK; 784 } 785 return this; 786 } 787 788 private native Throwable fillInStackTrace(int dummy); 789 790 /** 791 * Provides programmatic access to the stack trace information printed by 792 * {@link #printStackTrace()}. Returns an array of stack trace elements, 793 * each representing one stack frame. The zeroth element of the array 794 * (assuming the array's length is non-zero) represents the top of the 795 * stack, which is the last method invocation in the sequence. Typically, 796 * this is the point at which this throwable was created and thrown. 797 * The last element of the array (assuming the array's length is non-zero) 798 * represents the bottom of the stack, which is the first method invocation 799 * in the sequence. 800 * 801 * <p>Some virtual machines may, under some circumstances, omit one 802 * or more stack frames from the stack trace. In the extreme case, 803 * a virtual machine that has no stack trace information concerning 804 * this throwable is permitted to return a zero-length array from this 805 * method. Generally speaking, the array returned by this method will 806 * contain one element for every frame that would be printed by 807 * {@code printStackTrace}. Writes to the returned array do not 808 * affect future calls to this method. 809 * 810 * @return an array of stack trace elements representing the stack trace 811 * pertaining to this throwable. 812 * @since 1.4 813 */ 814 public StackTraceElement[] getStackTrace() { 815 return getOurStackTrace().clone(); 816 } 817 818 private synchronized StackTraceElement[] getOurStackTrace() { 819 // Initialize stack trace field with information from 820 // backtrace if this is the first call to this method 821 if (stackTrace == UNASSIGNED_STACK || 822 (stackTrace == null && backtrace != null) /* Out of protocol state */) { 823 int depth = getStackTraceDepth(); 824 stackTrace = new StackTraceElement[depth]; 825 for (int i=0; i < depth; i++) 826 stackTrace[i] = getStackTraceElement(i); 827 } else if (stackTrace == null) { 828 return UNASSIGNED_STACK; 829 } 830 return stackTrace; 831 } 832 833 /** 834 * Sets the stack trace elements that will be returned by 835 * {@link #getStackTrace()} and printed by {@link #printStackTrace()} 836 * and related methods. 837 * 838 * This method, which is designed for use by RPC frameworks and other 839 * advanced systems, allows the client to override the default 840 * stack trace that is either generated by {@link #fillInStackTrace()} 841 * when a throwable is constructed or deserialized when a throwable is 842 * read from a serialization stream. 843 * 844 * <p>If the stack trace of this {@code Throwable} {@linkplain 845 * Throwable#Throwable(String, Throwable, boolean, boolean) is not 846 * writable}, calling this method has no effect other than 847 * validating its argument. 848 * 849 * @param stackTrace the stack trace elements to be associated with 850 * this {@code Throwable}. The specified array is copied by this 851 * call; changes in the specified array after the method invocation 852 * returns will have no affect on this {@code Throwable}'s stack 853 * trace. 854 * 855 * @throws NullPointerException if {@code stackTrace} is 856 * {@code null} or if any of the elements of 857 * {@code stackTrace} are {@code null} 858 * 859 * @since 1.4 860 */ 861 public void setStackTrace(StackTraceElement[] stackTrace) { 862 // Validate argument 863 StackTraceElement[] defensiveCopy = stackTrace.clone(); 864 for (int i = 0; i < defensiveCopy.length; i++) { 865 if (defensiveCopy[i] == null) 866 throw new NullPointerException("stackTrace[" + i + "]"); 867 } 868 869 synchronized (this) { 870 if (this.stackTrace == null && // Immutable stack 871 backtrace == null) // Test for out of protocol state 872 return; 873 this.stackTrace = defensiveCopy; 874 } 875 } 876 877 /** 878 * Returns the number of elements in the stack trace (or 0 if the stack 879 * trace is unavailable). 880 * 881 * package-protection for use by SharedSecrets. 882 */ 883 native int getStackTraceDepth(); 884 885 /** 886 * Returns the specified element of the stack trace. 887 * 888 * package-protection for use by SharedSecrets. 889 * 890 * @param index index of the element to return. 891 * @throws IndexOutOfBoundsException if {@code index < 0 || 892 * index >= getStackTraceDepth() } 893 */ 894 native StackTraceElement getStackTraceElement(int index); 895 896 /** 897 * Reads a {@code Throwable} from a stream, enforcing 898 * well-formedness constraints on fields. Null entries and 899 * self-pointers are not allowed in the list of {@code 900 * suppressedExceptions}. Null entries are not allowed for stack 901 * trace elements. A null stack trace in the serial form results 902 * in a zero-length stack element array. A single-element stack 903 * trace whose entry is equal to {@code new StackTraceElement("", 904 * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code 905 * stackTrace} field. 906 * 907 * Note that there are no constraints on the value the {@code 908 * cause} field can hold; both {@code null} and {@code this} are 909 * valid values for the field. 910 */ 911 private void readObject(ObjectInputStream s) 912 throws IOException, ClassNotFoundException { 913 s.defaultReadObject(); // read in all fields 914 if (suppressedExceptions != null) { 915 List<Throwable> suppressed = null; 916 if (suppressedExceptions.isEmpty()) { 917 // Use the sentinel for a zero-length list 918 suppressed = SUPPRESSED_SENTINEL; 919 } else { // Copy Throwables to new list 920 suppressed = new ArrayList<>(1); 921 for (Throwable t : suppressedExceptions) { 922 // Enforce constraints on suppressed exceptions in 923 // case of corrupt or malicious stream. 924 if (t == null) 925 throw new NullPointerException(NULL_CAUSE_MESSAGE); 926 if (t == this) 927 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE); 928 suppressed.add(t); 929 } 930 } 931 suppressedExceptions = suppressed; 932 } // else a null suppressedExceptions field remains null 933 934 /* 935 * For zero-length stack traces, use a clone of 936 * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to 937 * allow identity comparison against UNASSIGNED_STACK in 938 * getOurStackTrace. The identity of UNASSIGNED_STACK in 939 * stackTrace indicates to the getOurStackTrace method that 940 * the stackTrace needs to be constructed from the information 941 * in backtrace. 942 */ 943 if (stackTrace != null) { 944 if (stackTrace.length == 0) { 945 stackTrace = UNASSIGNED_STACK.clone(); 946 } else if (stackTrace.length == 1 && 947 // Check for the marker of an immutable stack trace 948 SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) { 949 stackTrace = null; 950 } else { // Verify stack trace elements are non-null. 951 for(StackTraceElement ste : stackTrace) { 952 if (ste == null) 953 throw new NullPointerException("null StackTraceElement in serial stream. "); 954 } 955 } 956 } else { 957 // A null stackTrace field in the serial form can result 958 // from an exception serialized without that field in 959 // older JDK releases; treat such exceptions as having 960 // empty stack traces. 961 stackTrace = UNASSIGNED_STACK.clone(); 962 } 963 } 964 965 /** 966 * Write a {@code Throwable} object to a stream. 967 * 968 * A {@code null} stack trace field is represented in the serial 969 * form as a one-element array whose element is equal to {@code 970 * new StackTraceElement("", "", null, Integer.MIN_VALUE)}. 971 */ 972 private synchronized void writeObject(ObjectOutputStream s) 973 throws IOException { 974 // Ensure that the stackTrace field is initialized to a 975 // non-null value, if appropriate. As of JDK 7, a null stack 976 // trace field is a valid value indicating the stack trace 977 // should not be set. 978 getOurStackTrace(); 979 980 StackTraceElement[] oldStackTrace = stackTrace; 981 try { 982 if (stackTrace == null) 983 stackTrace = SentinelHolder.STACK_TRACE_SENTINEL; 984 s.defaultWriteObject(); 985 } finally { 986 stackTrace = oldStackTrace; 987 } 988 } 989 990 /** 991 * Appends the specified exception to the exceptions that were 992 * suppressed in order to deliver this exception. This method is 993 * thread-safe and typically called (automatically and implicitly) 994 * by the {@code try}-with-resources statement. 995 * 996 * <p>The suppression behavior is enabled <em>unless</em> disabled 997 * {@linkplain #Throwable(String, Throwable, boolean, boolean) via 998 * a constructor}. When suppression is disabled, this method does 999 * nothing other than to validate its argument. 1000 * 1001 * <p>Note that when one exception {@linkplain 1002 * #initCause(Throwable) causes} another exception, the first 1003 * exception is usually caught and then the second exception is 1004 * thrown in response. In other words, there is a causal 1005 * connection between the two exceptions. 1006 * 1007 * In contrast, there are situations where two independent 1008 * exceptions can be thrown in sibling code blocks, in particular 1009 * in the {@code try} block of a {@code try}-with-resources 1010 * statement and the compiler-generated {@code finally} block 1011 * which closes the resource. 1012 * 1013 * In these situations, only one of the thrown exceptions can be 1014 * propagated. In the {@code try}-with-resources statement, when 1015 * there are two such exceptions, the exception originating from 1016 * the {@code try} block is propagated and the exception from the 1017 * {@code finally} block is added to the list of exceptions 1018 * suppressed by the exception from the {@code try} block. As an 1019 * exception unwinds the stack, it can accumulate multiple 1020 * suppressed exceptions. 1021 * 1022 * <p>An exception may have suppressed exceptions while also being 1023 * caused by another exception. Whether or not an exception has a 1024 * cause is semantically known at the time of its creation, unlike 1025 * whether or not an exception will suppress other exceptions 1026 * which is typically only determined after an exception is 1027 * thrown. 1028 * 1029 * <p>Note that programmer written code is also able to take 1030 * advantage of calling this method in situations where there are 1031 * multiple sibling exceptions and only one can be propagated. 1032 * 1033 * @param exception the exception to be added to the list of 1034 * suppressed exceptions 1035 * @throws IllegalArgumentException if {@code exception} is this 1036 * throwable; a throwable cannot suppress itself. 1037 * @throws NullPointerException if {@code exception} is {@code null} 1038 * @since 1.7 1039 */ 1040 public final synchronized void addSuppressed(Throwable exception) { 1041 if (exception == this) 1042 throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception); 1043 1044 if (exception == null) 1045 throw new NullPointerException(NULL_CAUSE_MESSAGE); 1046 1047 if (suppressedExceptions == null) // Suppressed exceptions not recorded 1048 return; 1049 1050 if (suppressedExceptions == SUPPRESSED_SENTINEL) 1051 suppressedExceptions = new ArrayList<>(1); 1052 1053 suppressedExceptions.add(exception); 1054 } 1055 1056 private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0]; 1057 1058 /** 1059 * Returns an array containing all of the exceptions that were 1060 * suppressed, typically by the {@code try}-with-resources 1061 * statement, in order to deliver this exception. 1062 * 1063 * If no exceptions were suppressed or {@linkplain 1064 * #Throwable(String, Throwable, boolean, boolean) suppression is 1065 * disabled}, an empty array is returned. This method is 1066 * thread-safe. Writes to the returned array do not affect future 1067 * calls to this method. 1068 * 1069 * @return an array containing all of the exceptions that were 1070 * suppressed to deliver this exception. 1071 * @since 1.7 1072 */ 1073 public final synchronized Throwable[] getSuppressed() { 1074 if (suppressedExceptions == SUPPRESSED_SENTINEL || 1075 suppressedExceptions == null) 1076 return EMPTY_THROWABLE_ARRAY; 1077 else 1078 return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY); 1079 } 1080 }